APPLICABILITY OF RECYCLED ALKALINE WASTE MATERIALS FOR NEUTRALIZATION OF ACIDIC HOT SPRING WASTEWATER

Acidic wastewater including mining leachate and hot spring water can seriously affect surrounding ecosystems and natural environments in river basins. The wastewater is generally characterized by lower pH levels and higher concentrations of harmful elements such as arsenic (As) and lead (Pb). On the other hand, the discharge of waste materials has increased significantly in recent years, and thus, effective use of waste materials is urgently needed to contribute to the progress of the circular economy and sustainable development goals. The objective of this study is therefore to evaluate the applicability of recycled alkaline waste materials as alternative liming agents for the neutralization of acidic hot spring wastewater.

In the laboratory, batch wastewater neutralization experiments were performed using recycled alkaline waste materials such as recycled concrete, steel slug, wood ash, and calcium carbonate (as reference). In other words, a constant volume of wastewater was mixed with the recycled materials. Solid-liquid ratios ranging from 1:10 to 1:4000 were maintained. Supernatants were extracted by centrifugation after shaking for 10 minutes, corresponding to the neutralization reaction time. Then, pH, electric conductivity, and concentrations of harmful elements were measured immediately. For the precipitated materials after neutralization, the leachability of As and Pb was investigated based on conventional leaching experiments.

The neutralization and removal performance of As and Pb using recycled concrete and steel slug was higher than that of other recycled materials. Also, good stability of As and Pb was observed for the precipitated materials using both recycled concrete and steel slug, suggesting that these two alternative liming agents have higher applicability to neutralize hot spring wastewater.